ANTIOCH -- A 15-year-old boy recently pleaded no contest in Contra Costa County juvenile court to a murder charge in the beating death of an elderly man outside an Antioch hardware store last May, according to the district attorney's office.

Antioch police say the teen beat 83-year-old Patrick Chang on May 18 during a robbery in the parking lot of the Orchard Supply Hardware on Lone Tree Way. Chang, of Antioch, died from his injuries almost a month later.

The teen was held in juvenile hall on robbery charges for months while the district attorney's office awaited a full autopsy report and arraigned on a murder charge in October.

All other charges were dropped against the teen following the Jan. 8 plea, according to the district attorney's office.

The teen remains in juvenile hall. He returns to court for sentencing 1:30 p.m. on Feb. 21.

In a message posted on Facebook Tuesday, Police Chief Allan Cantando lauded the community's work for helping police detectives make an arrest within a week. The department sought help by sharing a surveillance photo on Facebook, hoping someone could identify the person responsible for the "horrific crime," Cantando said.

"You guys came up big," he said. "I want to thank everyone who helped bring some closure to this tragic event."